Refractory article and composition for and method of making same



Patented Aug. 11,1931

UNITED STATES PATENT OFFICE RICHARD H. MARTIN, -01 WORCESTER, MASSACHUSETTS, ASSIGNOR TD NORTON CON:-

PANY, F WORCESTER, MASSACHUSETTS, A. CORPORATION OF MASSACHUSETTS BEI'BAG'IDBY ARTICLE COMPOSITION FOR AN D METHOD OF SAME.

Ho Drawing.

This invention relates to refractories and more particularly to a refractory article having a protective coating thereover, as well as to a method of coating and protecting 3 such an article. l Certain refractory articles, such' as bricks saggers, and muflies are made of grains 0 a refractory material, such as crystalline alumina, bonded by ceramic materials vitrim fied to a vitreous or porcelainic condition, or

in the case of silicon carbide, by a recrystallization process which unites the crystals into a ri 'd structure. When such articles are use under certain conditions, \such for v141s example, as in an oil-fired furnace, the refractor' articles are exposed to the action of the urnace gases which often contain alkaline vapors. The alkaline vapors readily attack the ceramic bond'of the refractory so article and cause the same to deteriorate ra idly.

urthermore, it has been found that a refractory article made of silicon carbide tends to decompose when subjected to a high temperature in an oxidizing atmosphere, so that if the article is used as a sagger to hold white ware-"to be fired,-or is otherwise in proximity thereto, discoloration of such ware wil resul This decomposition causes the formation. of a slag coatigg or glaze of low refractoriness upon the icon carbide article, .which temporarily protects the article but during firing runs 05 permitting further decom' osition and slag formation. This weakens t e structure of the article and shortens its life of active service. It is an object of the invention to overcome such difiiculties, and provide an improved refractory article which will not be sub'ect to undue deterioration and which w' have highly refractory be capable of withstanding 'ig tures throughout its useful life.

A further'object is to provide a composition which may be employedas a protective coating for such articles, and particularly, to provide a method of coating such articles, so they may become more immune to the destructive action of the furnace gases.

In accordance with the invention I have temperapro erties and Application filed m 81, 1925. Serial m. 47,374.

found that a refractory body may be protected by a coatin com osed either wholl or in part of a big y re actory oxide, suc

as z'irconia. I have found that such. a coatv in effectively protects such articles, is not a ected by the furnace gases and is capable of resisting theheat treatment to which the article may be subjected. The refractory oxide may be used alone as a coating for the refractory body or may be combined with other suitable materials for bonding or holding the refractory oxide particles in the coating. The refractory oxide particles when brought to a suitable finely divided .condition tend to bond themselves together under normal ceramic operating conditions and with the article to be protected. It is often "preferable, however, to supplement such bonding action by mixing other-materials, such as a fusible constituent, to the refractory oxide which co-act therewith in.

some manner to bond or hold the same in the coating. Such other materials may include various ceramic bonding ingredients, such as the non-refractory silica in a suitable form, or one or more other suitable refractory oxides such as magnesia, which may be present either wholly or in part asimpurities or may beseparately added thereto. As one method of coating and thereby protecting a refractory article in accordance with the invention, a layer of thecoating material containing a refractory oxide either wholl or in part, previously thoroughly mixe with water to the desired plasticitly, may be applied thereon to a suitable thic ness depending upon the use to ,which the article is to be subjected. The article as thus made is then dried, and if desired may be used in this form, in which case the first firing operation serves to unite the refractor oxide particles into a coating; but prefera ly the article'is fired initially under an appropriate heat treatment to form theprotective layer on the article.

Preferably the refractory oxide or coating mixture is brought to a finely divided condition which assists the mechanical bonding the coating. It is feasible, as well as readily understood, that the coating mixture ma be applied upon the surface of the artic before the article has been fired, a

In certain instances, temporary bonding materials such as dextrine, gum, glue, resin y or other binders may be em loyed to facilitate the bonding of the re ractory oxide particles together and to the refractory article. These materials burn out during the subsequentfiring operation and leave only the refractor oxide coating.

As a speci ing capa le of protectin a refractory body, such as a mufile, made 0 crystalline alumina granules bonded into a porous mass by a vitrified ceramic bond, I may em loy a coating composition prepared by mixing 21% by wei ht of magnesia, having a grain size of 150 (150 meshes to the linear inch and finer) with 79% by weight of very finely divided zirkitecement (impure zirconium oxide) whose particles are such as to resemble colloids both in sizevand pro erties. The

refractory mixture-may then made into 25 a slip by the addition of an appropriate amount of water to form a liquid mixture of about the consistency of cream and painted on the refractory article. e article, v thus covered, is fired at about Orton cone 16 80 to form a relatively dense coating'thereon -which is substantially impervious to kiln gases under normal operating conditions.

- The zirkite cement employed in the above coating composition is an impure zirconium I5 oxide (ZrO having substantially the fol- 1 lowing composition:

SiO. 20. 8 A1 0 2. 01% 40 F 0,, 3.86% T10 0. 82% ZrO I 70. 9 CaO O. 10% Mg'O Trace. Loss on ignition 1 2. 17%

As the result of firing such a mixture, there is produced a dense coating which probably contains compounds of magnesia, zirconia, and silica, and the fusible constitl uents of the mixture serve to bond the other edients and hold them in place on the actory body beneath. The protective coatingof the invention containing a refractory oxide, such as zirconium oxide, serves as a surface layer which is in itself resistant todecomposition by the furnace and is insoluble in any alkaline vapors which may be resent therein,

and adequately protects the of the invention is more serviceable for various uses than theeordinary refractory article, since the coated article has all the desirable attributes of a bonded refractory 5 article while at the same time being immune 0 example of a refractory coaty of the refractory article beneath. The coated article to the destructive action of the furnace gases, in as much as the protective layer is substantially impervious to the furnace gases. The provisions of the invention are articularly advantageous for protecting re ractory articles composed of crystalline alumina united by a ceramic bond since such a bond is particularly sub'ect to deterioration by the action of the a aline vapors in furnacegases. Furthermore, it'will be readily a parent to one skilled in the art, that t e rovisions of the invention are advantageous or protecting'a silicon carbide refractory article which is subject to decomposition when subjected to oxidizing influences under hightem rature.

While the lnvention has been ecifically illustrated by describing one suitab e method of aplplying a specific coating composition, name one composed principally of zirconium oxide andcontaiinng magnesia, upon a refractory article made of crystalline alumina bonded with a ceramic bond, neverthe-- less, various equivalent coatin com ositions, 'will be readily apparent to t ose s 'lled in the art,- as well as the fact, that such coating compositions are suitably adapted for effectively protecting refractory articles of various com "ositions manufactured in accordance wit the usual customary practices.

This application contains sub ect matter in common with my Reissue atent No. 17,661, granted May 13, 1930.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: E

a relatively thincoatin thereon containing a ma'or roportion o? a zirconium compoun an a'fusible constituent.

2. A refractory article comprising a body of ceramic bonded crystalline alumina grains and a relatively thin coating thereon con taining as its largest ingredient a zirconium compound. c

3. A refractory article comprising a body of bonded, granular, refractory material and a relatively thin coating thereon which resists alkaline vapors, formed by firing in 1. A refractory article comprising a body of bonded, refractory, granular material and situ a mixture comprising magnesia and zirconia, the latter being the largest ingredient of the mixture.

4. A refractory body comprising ceramic bonded, refractory, granular material and a relatively thin coating thereon containing a predominating amount of zirconia and a smaller. amount of magnesia with associated impurities fired'in situ to form a relatively dense coating whichis substantially impervious to kiln gases under normal firing conditions. V

5. A refractory article comprising a body of ceramic bonded, crystalline alumina grains and a relatively thincoating thereon capable 'of resisting alkaline vapors which contains a major progortion of zirconia andbonding ingredients red in'situ.

6. A refractory article cdmprising a body 5 of bonded, granular, refractory material and a relatively thin coating thereon containing over 50% of zirconia and a smaller amount of a bonding ingredient capable of. uniting therewith and of forming a dense coating which resists penetration of alkaline va ors to the refractory body beneath.

A refractory articlecomprising a body of bonded,- refractory, granular material and a relatively thin coating thereon fired 15 in situ, which has a large (proportion of both magnesia and zirconia an a smaller amount of silica and associated impurities, the zirconia being the largest ingredient.

8. A refractory article comprising a body 20 of ceramic bonded crystalline alurmna-hav: ing a relativel thin coating thereonjcon taming a re ominating proportion of a compound ormed by firing in s1tu magnesia, zirconia and a fusible material, the zirconia being the largest ingredient.

9. A refractory article comprising a body of ceramic bonded crystalline alumina granules and a relatively thin protective coating-thereon containing compounds formed 50 by firing magnesia, zirconia and associated impuritles including silica at a sufliciently high tem ratur'eto form a dense coating thereof t e zirconium compound forming the ma or ortion of the coating. y

35 10. re ractory article comprisin abod of ceramic bonded refractory gran ar ma-' terial and a relatively thin protective coating thereon which ,is refractory to alkaline vapors,-formed by firing in situ'a composition containing a bond and of which a zirconium compound isthe largest ingredient.

Signed at Worcester, Massachusetts, this 

